A large swath infrared camera on-orbit calibration data processing method

Abstract

The application discloses a large-width swing-scan infrared camera in-orbit calibration data processing method, which utilizes cold space calibration data of each scanning strip of the infrared camera to correct the fluctuation of high-temperature blackbody calibration data and low-temperature blackbody calibration data in real time; the corrected high-temperature blackbody calibration data and low-temperature blackbody calibration data are subjected to blind element detection and blind element replacement; the high-temperature blackbody calibration data and low-temperature blackbody calibration data after blind element replacement are combined with a calibration correction model to obtain absolute radiation calibration coefficients at different scanning angles; a response fluctuation correction model at different scanning angles for earth observation is established based on cold space observation data; and the response fluctuation correction model is utilized to correct earth observation data to obtain real responses at different scanning angles for earth observation. The application can effectively inhibit calibration data fluctuation caused by large-width swing scan and provide a basis for subsequent quantitative inversion.

Description

Technical Field

[0001] This invention relates to the field of on-orbit absolute radiometric calibration technology for spaceborne infrared cameras, and in particular to a method for processing on-orbit calibration data of a wide-swath oscillating infrared camera. Background Technology

[0002] In-orbit absolute radiometric calibration of infrared cameras is fundamental to their quantitative applications, and on-board calibration is the preferred method for in-orbit absolute radiometric calibration. On-board calibration devices for wide-swath infrared cameras typically include high-temperature blackbody, low-temperature blackbody, and cold-space calibration sources. Within one scanning observation cycle, the infrared camera can acquire imaging data of Earth targets, high-temperature blackbody calibration data, low-temperature blackbody calibration data, and cold-space calibration data. However, due to the large scanning imaging angle of this type of camera, the acquired on-board calibration data exhibits significant fluctuations, such as… Figure 1 As shown, this presents a serious challenge to the accuracy and stability of the calibration.

[0003] Currently, most research on on-board calibration data processing for spaceborne infrared cameras focuses on absolute radiometric calibration based on stable on-board calibration data. Although some studies involve methods for correcting radiometric calibration data, on the one hand, their technical prerequisites and model parameters depend on controllable ground conditions; on the other hand, the correction models are based on the relationship between the temperature of various components of the remote sensor calibrated in the laboratory and the relative and absolute calibration of the on-board blackbody, without considering the influence of actual on-orbit factors such as changes in scanning angle and space environment disturbances during wide-swath imaging, and are not suitable for on-board calibration data processing of wide-swath imaging infrared cameras. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide an on-orbit calibration data processing method for a wide-swath sweep infrared camera, which effectively suppresses calibration data fluctuations caused by wide-swath sweep.

[0005] The technical solution of this invention is: an on-orbit calibration data processing method for a wide-swath infrared camera, used to obtain the absolute radiometric calibration coefficients at different scanning angles and the true response to the ground at different scanning angles, specifically as follows:

[0006] Using cold-air calibration data from each scan strip of the infrared camera, fluctuations in high-temperature and low-temperature blackbody calibration data are corrected in real time. Blind pixel detection and replacement are performed on the corrected high-temperature and low-temperature blackbody calibration data. Using the high-temperature and low-temperature blackbody calibration data after blind pixel replacement, combined with the calibration correction model, the absolute radiation calibration coefficients at different scanning angles are obtained.

[0007] Based on cold air observation data, a response fluctuation correction model for Earth observation under different scanning angles is established; using the response fluctuation correction model, the Earth observation data is corrected to obtain the true response under different scanning angles.

[0008] Furthermore, the real-time correction of fluctuations in the high-temperature blackbody calibration data and the low-temperature blackbody calibration data involves the following steps:

[0009] Calculate the mean value of the cold air calibration data for each scan strip, and use it as the cold air calibration data response benchmark;

[0010] Calculate the change in the cold air calibration data of each scan strip relative to the cold air calibration data baseline;

[0011] For a given scan strip, based on the change corresponding to that scan strip, the high-temperature blackbody calibration data and low-temperature blackbody calibration data for that scan strip are corrected, as follows:

[0012] DN′ hj =DN hj -k h ×ΔDN j

[0013] DN′ lj =DN lj -k l ×ΔDN j

[0014] ΔDN j The change in the cold air calibration data of the j-th scan strip relative to the cold air calibration data baseline;

[0015] DN hj The mean value of the high-temperature blackbody response for the j-th scan strip;

[0016] DN′ hj The response is the corrected response of the high-temperature blackbody in the j-th scan strip;

[0017] k h This is the ratio of the rate of change of the high-temperature blackbody response to the rate of change of the response of the cold air calibration data;

[0018] DN lj The mean value of the low-temperature blackbody response for the j-th scan strip;

[0019] DN′ lj The response is the corrected response of the low-temperature blackbody for the j-th scan strip;

[0020] k l This is the ratio of the rate of change of the low-temperature blackbody response to the rate of change of the cold air calibration data response.

[0021] Furthermore, the principle of blind pixel detection is: the pixel response is 0 or the response is saturated; or the pixel noise is greater than twice the mean noise.

[0022] Furthermore, the blind pixel replacement is specifically implemented by replacing the value of the blind pixel with the average value of the adjacent normal pixels.

[0023] Furthermore, by utilizing the high-temperature blackbody calibration data and low-temperature blackbody calibration data after blind element replacement, and combining them with the calibration correction model, the absolute radiation calibration coefficients for different scanning angles are obtained. The specific steps are as follows:

[0024] Based on the high-temperature blackbody calibration data and low-temperature blackbody calibration data after blind cell replacement, the mean temperature T of the high-temperature blackbody is calculated. H Low-temperature blackbody temperature mean T L and the mean DN of high temperature blackbody response H Mean DN of low temperature blackbody response L ;

[0025] Based on the average temperature T obtained in the previous step H T L Calculate the equivalent radiance value Le of the high-temperature blackbody spectrum in each spectral band. H Low-temperature blackbody spectral equivalent radiance value Le L ;

[0026] Calculate the absolute calibration equation at the on-board calibration blackbody:

[0027]

[0028] C N =Le H -K N ×DN H

[0029] Using K N and C N Substituting these values ​​into the calibration correction model, we obtain the absolute radiometric calibration coefficients for different scanning angles, including the absolute calibration slope coefficient and the absolute calibration intercept coefficient.

[0030] Furthermore, based on cold air observation data, a response fluctuation correction model is established for Earth observations under different scanning angles. The specific steps are as follows:

[0031] Satellite maneuvering imaging acquires Earth observation field of view and cold space observation data DN SV ;

[0032] Based on the high-temperature blackbody calibration data from this maneuver imaging, the slope Z of its change over time was calculated. H ;

[0033] Calculate the cold air observation data DN at different scanning angles for Earth observation. SV The slope Z(θ) as a function of time;

[0034] Establish the relationship R(θ) between the slope of cold air observation data over time and the slope of high-temperature blackbody calibration data.

[0035]

[0036] Furthermore, the Earth observation data is corrected to obtain the true response at different scanning angles. The specific method is as follows:

[0037] DN′ θj =DN θj -R(θ)×k h ×ΔDN j

[0038] In the formula,

[0039] DN′ θj This is the corrected response at the scanning angle θ of the j-th scan strip;

[0040] DN θj This is the response at the scanning angle θ of the j-th scan strip;

[0041] k h This is the ratio of the rate of change of the high-temperature blackbody response to the rate of change of the response of the cold air calibration data;

[0042] ΔDN j denoted as the change in the cold air calibration data of the j-th scan strip relative to the cold air calibration data baseline.

[0043] The present invention also relates to a computer program product that, when executed by a processor, implements the steps of the method as described above.

[0044] The present invention also relates to an on-board computing terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method as described above.

[0045] The advantages of this invention compared to the prior art are:

[0046] (1) This invention is the first to propose a method for correcting the fluctuations of on-board high and low temperature blackbody calibration data based on cold space observation;

[0047] (2) This invention takes into account the correction of fluctuations in Earth observation data, establishes a data fluctuation correction model under different scanning angles of Earth observation, and finally obtains a real and effective response to Earth observation. Attached Figure Description

[0048] Figure 1 This is a diagram illustrating the fluctuations in calibration data.

[0049] Figure 2 This is a flowchart of the method of the present invention;

[0050] Figure 3 A comparison chart showing the calibration data before and after correction. Detailed Implementation

[0051] To better understand the technical solution of the present invention, the specific embodiments of the present invention are described below.

[0052] The on-orbit calibration data processing method for a wide-swath infrared camera proposed in this invention has the following main steps: Figure 2 As shown, it includes:

[0053] Step 1: Use the cold space calibration data of each scan strip of the infrared camera to correct the fluctuations of the high and low temperature blackbody calibration data on the satellite in real time.

[0054] The specific steps are as follows:

[0055] (1.1) Calculate the mean value of the cold air calibration data for each scan strip as the baseline response value;

[0056]

[0057] In the formula, DN0 is the cold air calibration data response benchmark;

[0058] M represents the number of scan strips during a certain period of time in orbit;

[0059] DN Si is the mean of the cold air calibration data for the i-th scan strip.

[0060] (1.2) Calculate the change in cold air calibration data of each scan strip relative to the baseline response value based on the following formula;

[0061] ΔDN j =DN Sj -DN0 (2)

[0062] ΔDN j The change in the cold air calibration data of the j-th scan strip relative to the baseline;

[0063] DN Sj The cold air calibration mean of the j-th scan strip

[0064] (1.3) Based on the ΔDN obtained in the previous step j The high and low temperature blackbodies of the scanned band are corrected accordingly.

[0065] DN′hj =DN hj -k h ×ΔDN j (3)

[0066] DN′ lj =DN lj -k l ×ΔDN j (4)

[0067] DN hj The mean value of the high-temperature blackbody response for the j-th scan strip;

[0068] DN′ hj The response is the corrected response of the high-temperature blackbody in the j-th scan strip;

[0069] DN lj The mean value of the low-temperature blackbody response for the j-th scan strip;

[0070] DN′ lj The response is the corrected response of the low-temperature blackbody for the j-th scan strip;

[0071] k h This is the ratio of the rate of change of the on-board high-temperature blackbody response to the rate of change of the cold-space calibration data response;

[0072] k l This is the ratio of the rate of change of the on-board low-temperature blackbody response to the rate of change of the cold space calibration data response.

[0073] Figure 3 A schematic diagram showing the comparison of DN fluctuation curves before and after on-board calibration data correction is provided. Figure 3 It can be seen that this step can effectively resolve the fluctuations in on-board calibration data.

[0074] Step 2: Perform blind pixel detection and blind pixel replacement based on the corrected high and low temperature blackbody calibration data.

[0075] The blind pixel detection standard is: one of the following conditions must be met: (1) the pixel response is 0 or the response is saturated; (2) the pixel noise is greater than twice the mean noise.

[0076] The specific method of blind cell replacement is as follows:

[0077] Assuming the i-th element is a blind element, the following formula is used for blind element replacement:

[0078] DN″ hj (i)=DN′ hj (i-1) / 2+DN′ hj (i+1) / 2 (5)

[0079] DN″ lj (i)=DN′lj (i-1) / 2+DN′ lj (i+1) / 2 (6)

[0080] DN″ hj (i) DN″ lj (i) represents the response DN value of the i-th pixel after blind pixel replacement in the j-th scan strip of the calibration data for high-temperature blackbody and low-temperature blackbody, respectively.

[0081] Step 3: Using the high-temperature blackbody calibration data and low-temperature blackbody calibration data after blind element replacement, combined with the calibration correction model, the absolute radiation calibration coefficients for different scanning angles are obtained.

[0082] (3.1) High and low temperature blackbody calibration data DN based on blind element replacement h "、DN l ″, calculate its average temperature T H T L and the mean response DN H DN L ;

[0083] (3.2) Based on the average high and low temperature blackbody temperature T obtained in the previous step H T L Calculate the equivalent radiance values ​​Le of the high and low temperature blackbody spectra in each spectral band. H Le L ;

[0084]

[0085] In the formula:

[0086] Le — Spectral radiance (W / sr.m) 2 );

[0087] T – Absolute temperature (K);

[0088] λ — wavelength (μm);

[0089] ε — Target emissivity;

[0090] λ1, λ2 — starting wavelength and cutoff wavelength (μm);

[0091] c1=2πhc 2 =3.7415x10 8 Wm -2 .μm 4 ;

[0092] c² = hc·10 / k = 1.43879x10 4 μm.K.

[0093] (3.3) Based on the results obtained in the previous step, calculate the absolute calibration equation at the blackbody on the star, as shown in the following equation.

[0094]

[0095] C N =Le H -K N ×DN H (9)

[0096] In the formula,

[0097] K N is the absolute calibration slope coefficient at the blackbody on the star;

[0098] C N This is the absolute calibration intercept coefficient at the blackbody on the star.

[0099] (3.4) Using K N and C N Substituting these values ​​into the calibration correction model, we obtain the absolute radiometric calibration coefficients for different scanning angles, including the absolute calibration slope coefficient and the absolute calibration intercept coefficient.

[0100] (K Wθ C Wθ )=F′(K N C N ,θ) (10)

[0101] In the formula,

[0102] K Wθ This is the absolute calibration slope coefficient at the Earth observation scanning angle θ;

[0103] C Wθ This is the absolute calibration intercept coefficient at the Earth observation scanning angle θ.

[0104] θ is the Earth observation scanning angle;

[0105] F′ is the calibration correction model.

[0106] The calibration correction model F′ is generally an m-th degree polynomial: F′=a m θ m +a m-1 θ m-1 +...+a1θ+a0, where the polynomial degree m is generally referenced from laboratory calibration results, and a0, a1, ..., a m These are the coefficients of the polynomial.

[0107] Step 4: Based on cold air observation data, establish a response fluctuation correction model for Earth observation under different scanning angles.

[0108] (4.1) Satellite maneuvering imaging to acquire Earth observation field of view and cold space observation data DN SV ;

[0109] (4.2) Calculate the slope Z of the high-temperature blackbody calibration data generated during satellite maneuvering imaging as a function of time. H ;

[0110] (4.3) Calculate the slope Z(θ) of cold air observation data over time under different scanning angles of Earth observation.

[0111] (4.4) Establish the multiple relationship R(θ) between the slope of change of the Earth observation angle under different scanning angles and the slope of change of the high temperature blackbody.

[0112]

[0113] Step 5: Based on the model obtained in the previous step, the Earth observation data is corrected to obtain the true response of the Earth under different scanning angles.

[0114] DN′ θj =DN θj -R(θ)×ΔDN hj =DN θj -R(θ)×k h ×ΔDN j (13)

[0115] In the formula,

[0116] DN θj This is the response at the scanning angle θ of the j-th scan strip;

[0117] DN′ θj This is the corrected response at the scanning angle θ of the j-th scan strip.

[0118] This concludes the processing method. The absolute radiometric calibration coefficients obtained in step 3 for different scanning angles and the true responses to the Earth at different scanning angles obtained in step 5 are provided to subsequent calibration application processes as the basis for quantitative inversion.

[0119] It is understood that this invention has been described through embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific circumstances without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are protected by this invention.

[0120] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for processing on-orbit calibration data of a wide-swath infrared camera, characterized in that, The method used to obtain the absolute radiometric calibration coefficients at different scanning angles and the true response to the ground at different scanning angles is as follows: Using cold-air calibration data from each scan strip of the infrared camera, fluctuations in high-temperature and low-temperature blackbody calibration data are corrected in real time. Blind pixel detection and replacement are performed on the corrected high-temperature and low-temperature blackbody calibration data. Using the high-temperature and low-temperature blackbody calibration data after blind pixel replacement, combined with the calibration correction model, the absolute radiation calibration coefficients at different scanning angles are obtained. Based on cold air observation data, a response fluctuation correction model for Earth observation under different scanning angles is established. The response fluctuation correction model is used to correct the Earth observation data to obtain the true response of the Earth at different scanning angles.

2. The on-orbit calibration data processing method for a wide-swath infrared camera according to claim 1, characterized in that: The specific steps for real-time correction of fluctuations in high-temperature and low-temperature blackbody calibration data are as follows: Establish a baseline for cold air calibration data response; Calculate the change in the cold air calibration data of each scan strip relative to the cold air calibration data baseline; For a given scan strip, based on the change corresponding to that scan strip, the high-temperature blackbody calibration data and low-temperature blackbody calibration data for that scan strip are corrected, as follows: DN′ hj =DN hj -k h ×ΔDN j DN′ lj =DN lj -k l ×ΔDN j ΔDN j The change in the cold air calibration data of the j-th scan strip relative to the cold air calibration data baseline; DN hj The mean value of the high-temperature blackbody response for the j-th scan strip; DN′ hj The response is the corrected response of the high-temperature blackbody in the j-th scan strip; k h This is the ratio of the rate of change of the high-temperature blackbody response to the rate of change of the response of the cold air calibration data; DN lj The mean value of the low-temperature blackbody response for the j-th scan strip; DN′ lj The response is the corrected response of the low-temperature blackbody for the j-th scan strip; k l This is the ratio of the rate of change of the low-temperature blackbody response to the rate of change of the cold air calibration data response.

3. The on-orbit calibration data processing method for a wide-swath infrared camera according to claim 1, characterized in that: The principle of blind pixel detection is: the pixel response is 0 or the response is saturated; or the pixel noise is greater than twice the mean noise.

4. The on-orbit calibration data processing method for a wide-swath infrared camera according to claim 1, characterized in that: The blind pixel replacement is specifically performed by replacing the value of the blind pixel with the mean of the adjacent normal pixels.

5. The on-orbit calibration data processing method for a wide-swath infrared camera according to claim 1, characterized in that: The absolute radiation calibration coefficients for different scanning angles are obtained by using the high-temperature blackbody calibration data and low-temperature blackbody calibration data after blind element replacement, combined with the calibration correction model. The specific steps are as follows: Based on the high-temperature blackbody calibration data and low-temperature blackbody calibration data after blind cell replacement, the mean temperature T of the high-temperature blackbody is calculated. H Low-temperature blackbody temperature mean T L and the mean DN of high temperature blackbody response H Mean DN of low temperature blackbody response L ; Based on the average temperature T obtained in the previous step H T L Calculate the equivalent radiance value Le of the high-temperature blackbody spectrum in each spectral band. H Low-temperature blackbody spectral equivalent radiance value Le L ; Calculate the absolute calibration equation at the on-board calibration blackbody: C N =The H -K N ×DN H Using K N and C N Substituting these values ​​into the calibration correction model, we obtain the absolute radiometric calibration coefficients for different scanning angles, including the absolute calibration slope coefficient and the absolute calibration intercept coefficient.

6. The on-orbit calibration data processing method for a wide-swath infrared camera according to claim 1, characterized in that: The specific steps for establishing a response fluctuation correction model for Earth observations under different scanning angles based on cold air observation data are as follows: Satellite maneuvering imaging acquires Earth observation field of view and cold space observation data DN SV ; Based on the high-temperature blackbody calibration data from this maneuver imaging, the slope Z of its change over time was calculated. H ; Calculate the cold air observation data DN at different scanning angles for Earth observation. SV The slope Z(θ) as a function of time; Establish the relationship R(θ) between the slope of cold air observation data over time and the slope of high-temperature blackbody calibration data.

7. The on-orbit calibration data processing method for a wide-swath infrared camera according to claim 6, characterized in that: The Earth observation data is corrected to obtain the true response at different scanning angles. The specific method is as follows: DN′ θj =DN θj -R(θ)×k h ×ΔDN j In the formula, DN′ θj This is the corrected response at the scanning angle θ of the j-th scan strip; DN θj This is the response at the scanning angle θ of the j-th scan strip; k h This is the ratio of the rate of change of the high-temperature blackbody response to the rate of change of the response of the cold air calibration data; ΔDN j denoted as the change in the cold air calibration data of the j-th scan strip relative to the cold air calibration data baseline.

8. A computer program product, characterized in that: When the computer program product is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 7.

9. An on-board computing terminal, characterized in that: It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method as described in any one of claims 1 to 7.

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